This invention relates to a testing device for testing a measuring device. In particular, this invention relates to a calibration member for use in calibrating an optical scanner before the optical scanner is used for detection of foreign particles or flaws on a surface of a substrate and to a method of manufacturing the calibration member.
On manufacturing a semiconductor integrated circuit, a semiconductor substrate is used to form a wide variety of circuit elements. At any rate, the semiconductor substrate should have a clean principal surface. In other words, any foreign particles, such as dust or dirt, and flaws must be removed from the principal surface so as to manufacture the circuit elements having desired characteristics. Therefore, it is necessary that such foreign particles and flaws are measured and detected with high sensitivity on the principal surface of each semiconductor substrate.
An optical scanner is used to measure sizes of the foreign particles and the flaws and comprises an optical scanning portion for scanning the principal surface by a laser beam and a photodetector for detecting light reflected and scattered on the principal surface of the semiconductor substrate. However, it is to be noted here that each optical scanner might have sensitivity variable in dependency upon an optical characteristic of each photodetector and upon an atmospheric condition of measurement.
Under the circumstances, each optical scanner must be calibrated to determine the sensitivity before the foreign particles and/or flaws are measured in connection with the semiconductor substrate. Calibration is carried out by the use of a calibration member which has standard patterns of desired sizes and thicknesses. The standard patterns may be called dummy foreign particles or dummy patterns because they are formed instead of the foreign particles on the semiconductor substrate.
A conventional calibration member has the dummy patterns which are formed by etching a semiconductor wafer on a wafer surface by the use of a photolithographic technique. It is mentioned here that an etch rate is liable to be varied, depending upon an etching time, concentration and temperature of an etchant, and the like. Accordingly, it is difficult to adjust the thicknesses of the dummy patterns of each calibration member to the desired thickness. This shows that the dummy patterns of each calibration member may be different in thickness from those of the other calibration members. As a result, such differences of thicknesses of the dummy patterns make it difficult to accurately calibrate the optical scanner.
In the U.S. Pat. No. 4,512,659, a calibration member is revealed by Galbraith et al to calibrate the optical scanner and comprises a semiconductor wafer coated with a thin layer of oxide or nitride. The thin layer is partially removed to form the dummy patterns. The thicknesses of the dummy patterns may be adjusted to a desired thickness in each calibration member.
In the meanwhile, such a calibration member might be applied not only to calibration of a semiconductor device but also to calibration of a photomask or a photomask blank. On application of the above-mentioned conventional calibration member to calibration of the photomask or photomask blank, inconvenience takes place because light scattered from the photomask or photomask blank is noticeably different from that scattered from the semiconductor device.
In addition, the conventional calibration member is expensive because of use of a refined semiconductor wafer.